Liquid crystal display device and method of fabricating the same

ABSTRACT

There is provided a liquid crystal display device including (a) a pixel electrode, (b) a first signal line extending along one side of the pixel electrode, and (c) a second signal line extending along the other side of the pixel electrode. A first length along which the pixel electrode and the first signal line are adjacent to each other is equal to a second length along which the pixel electrode and the second signal line are adjacent to each other, a first space between the pixel electrode and the first signal line is equal to a second space between the pixel electrode and the second signal line. The liquid crystal display device makes it possible to minimize imbalance in parasitic capacitances to be generated between the pixel electrode and the first and second signal lines.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a liquid crystal display device and a method offabricating the same, and more particularly to a liquid crystal displaydevice which is capable of eliminating variance in parasitic capacitanceto be generated between a pixel electrode and signal lines, and a methodof fabricating such a liquid crystal display device.

2. Description of the Related Art

A liquid crystal display device has recently drawn attention as a thinand low power-consumption display to be substituted for a conventionalcathode ray tube. In particular, a so-called active matrix type liquidcrystal display device, which employs a non-linear device such as a thinfilm transistor (TFT) and a metal insulator metal (MIM) type transistoras a driver element, has drawn attention due to high quality in display.

Hereinbelow is explained an operation of a conventional liquid crystaldisplay device with reference to FIG. 1 which is a circuit diagram of acircuit equivalent to a pixel.

As illustrated in FIG. 1, a thin film transistor (TFT) 14 is comprisedof a drain electrode 14 a electrically connected to a first signal line11 i, a source electrode 14 b, and a gate electrode 14 c electricallyconnected to a scanning line 12. A pixel electrode 13 is electricallyconnected to the source electrode 14 b. A liquid crystal capacitance 32having a capacity of C_(LC) and including liquid crystal agent asdielectric material is formed between the pixel electrode 13 and anopposing electrode 33 formed on an opposing substrate.

A liquid crystal display device is generally designed to have aplurality of scanning lines 12 (only one of them is illustrated inFIG. 1) to which a scanning signal is successively applied. In a periodother than a scanning period, a scanning signal is not applied to thescanning lines 12, and hence, the drain electrode 14 a and the sourceelectrode 14 b are electrically insulated from each other. In a scanningperiod, a scanning signal is applied to the scanning lines 12. Thescanning signal activates a channel of the thin film transistor 14, andthus, the drain electrode 14 a and the source electrode 14 b areelectrically connected to each other. At the same time, a signal isapplied to the first signal line 11 i in accordance with a voltage to beapplied to the liquid crystal capacitance 32, which is charged by thesignal.

After a scanning period has been over, a scanning signal is no longerapplied to the scanning lines 12, resulting in that the drain electrodes14 a and the source electrodes 14 b become electrically insulated fromeach other again. Hence, the liquid crystal capacitance 32 is keptcharged, and thus, it is possible to optically control liquid crystal bymeans of an electric field generated between the opposing electrode 33and the pixel electrode 13.

In a period other than a scanning period, a quite small amount ofcurrent, which is so-called leakage current, flows between the drainelectrode 14 a and the source electrode 14 b. The leakage currentreduces a difference in voltage between the pixel electrode 13 and theopposing electrode 33 until a next scanning period. If such a differencein voltage is not reduced, there would caused degradation in contrast,resulting in reduction in display quality.

In order to avoid such degradation in contrast, an auxiliary capacitance34 having a capacity of C_(s) is additionally inserted in parallel withthe liquid crystal capacitance 32 to thereby prevent reduction involtage. In the liquid crystal display device illustrated in FIG. 1, theauxiliary capacitance 34 is provided in parallel with the pixelelectrode 13 and the thin film transistor 14.

The auxiliary capacitance 34 may be provided at other locations, unlessthe auxiliary capacitance 34 is in parallel with the liquid crystalcapacitance 32.

The liquid crystal display device is designed to include a plurality ofsuch pixels as illustrated in FIG. 1, in an array.

FIG. 2 is a plan view of a pixel of the liquid crystal display devicehaving the above-mentioned structure. In FIG. 2, the auxiliarycapacitance 34 illustrated in FIG. 1 is not illustrated for the sake ofsimplicity.

As illustrated in FIG. 2, the pixel electrode 13 is sandwiched betweenthe first and second signal lines 11 i and 11 j. In other words, thefirst signal line 11 i extends along one side of the pixel electrode 13,and the second signal line 11 j extends along the other side of thepixel electrode 13. Hence, there are generated a first parasiticcapacitance 16i having a capacity of Cd-pii between the pixel electrode13 and the first signal line 11 i, and a second parasitic capacitance 16j having a capacity of Cd-pij between the pixel electrode 13 and thesecond signal line 11 j.

The longer the length Li and Lj along which the pixel electrode 13 isadjacent to the first and second signal lines 11 i and 11 j are, or theshorter the spaces di and dj between the pixel electrode 13 and thefirst and second signal lines 11 i and 11 j are, the greater theparasitic capacitances 16 i and 16 j are. The parasitic capacitances 16i and 16 j cause a voltage of the pixel electrode 13 to be influenced byfluctuation in voltage of the first and second signal lines 11 i and 11j.

The fluctuation ΔVpi in voltage of the pixel electrode 13 is representedas follows.

ΔVpi=(Cd-pii×ΔVi+Cd-pij×ΔVj)/(C _(LC) +C _(s)+Cd-pii+Cd-pij)

In the equation, ΔVi and ΔVj represent fluctuation in voltage of thefirst and second signal lines 11 i and 11 j, respectively.

Hereinbelow is explained a method of driving the liquid crystal displaydevice illustrated in FIGS. 1 and 2.

It is desirable that an orientation of an electric field to be appliedto the liquid crystal capacitance 32, that is, a polarity of the pixelelectrode 13 is inverted every period for updating display. This isbecause if a polarity of the pixel electrode 13 is kept unchanged, therewould occur phenomenon called “burning” in which display is fixed whenthe same image is kept displayed, and display cannot be returned back tooriginal display. This degrades quality in display.

In addition, it is desired that polarity of the pixel electrodes isuniformly distributed in a screen of a liquid crystal display device.The reason is as follows. In an actual liquid crystal display device,there exists a slight difference in brightness in display in accordancewith positive or negative polarity of the pixel electrode 13. If thepolarity of the pixel electrode 13 in an entire screen alters betweenpositive and negative ones each time display is updated, brightness anddarkness are repeated, which remarkably deteriorates visibility.

For this reason, there have been suggested a lot of arrangements ofpolarity of pixel electrodes in a screen and a lot of methods of drivinga liquid crystal display device.

FIG. 3A illustrates polarity of pixel electrodes in a screen in acertain display updating period, and FIG. 3B illustrates polarity ofpixel electrodes in a screen in a next display updating period both ingate line inversion drive. Namely, FIGS. 3A and 3B show how polarity ofpixel electrodes vary in successive display updating periods in gateline inversion drive. Similarly, FIG. 4A illustrates polarity of pixelelectrodes in a screen in a certain display updating period, and FIG. 4Billustrates polarity of pixel electrodes in a screen in a next displayupdating period both in drain line inversion drive. Namely, FIGS. 4A and4B show how polarity of pixel electrodes vary in successive displayupdating periods in drain line inversion drive. FIG. 5A illustratespolarity of pixel electrodes in a screen in a certain display updatingperiod, and FIG. 5B illustrates polarity of pixel electrodes in a screenin a next display updating period both in dot inversion drive. Namely,FIGS. 5A and 5B show how polarity of pixel electrodes vary in successivedisplay updating periods in dot inversion drive.

Herein, the gate line inversion drive means a method of driving a liquidcrystal display device, in which pixel electrodes arranged in adirection in which scanning lines extend are designed to have the samepolarity, and those polarity are inverted each time display is to beupdated. The drain line inversion drive means a method of driving aliquid crystal display device, in which pixel electrodes arranged in adirection in which signal lines extend are arranged are designed to havethe same polarity, and those polarity are inverted each time display isto be updated. The dot inversion drive means a method of driving aliquid crystal display device, in which adjacent pixel electrodes aredesigned to have opposite polarity both in a direction in which scanninglines extend and both in a direction in which signal lines extend, andthose polarity are inverted each time display is to be updated.

In FIGS. 3A, 3B, 4A, 4B, 5A and 5B, pixel electrodes having a sign “+”are designed to have a positive polarity, whereas pixel electrodeshaving a sign “−” are designed to have a negative polarity.

When a liquid crystal display is driven in such a manner as illustratedin FIGS. 3A to 5B, fluctuation in voltage of the signal lines ismaximized when polarity of the signal lines are inverted. Accordingly,voltage of a pixel electrode is influenced most remarkably at that time,and hence, brightness is varied.

As is obvious in view of FIGS. 3A, 3B, 4A, 4B, 5A and 5B, adjacentsignal lines always have the same polarity in the gate line inversiondrive illustrated in FIGS. 3A and 3B. In contrast, adjacent signal linesalways have opposite polarity in both the drain line inversion driveillustrated in FIGS. 4A and 4B and the dot inversion drive illustratedin FIGS. 5A and 5B. Hence, influence caused by polarity inversion iscancelled each other in the drain line inversion drive and the dotinversion drive, and hence, it is possible to reduce fluctuation inbrightness of a pixel relative to the gate line inversion driveillustrated in FIGS. 3A and 3B.

However, such reduction in fluctuation in brightness of a pixel iseliminated, if the parasitic capacitances Cd-pii and Cd-pij generatedbetween the pixel electrode and the signal lines are quite differentfrom each other. Hence, the parasitic capacitances between the pixelelectrode and the signal lines have to be designed to have the samecapacity in order to minimize fluctuation in brightness of a pixel,caused by fluctuation in voltage of the signal lines.

As mentioned earlier, the thin film transistor 14 is turned on receiptof a scanning signal transmitted through the scanning line 12 in theconventional liquid crystal display device illustrated in FIG. 2. Thatis, the drain electrode 14 a is electrically communicated to the sourceelectrode 14 b. At that time, a liquid crystal capacitance and anauxiliary capacitance (not illustrated) both formed between the pixelelectrode 13 and the opposing electrode (not illustrated) are charged bya display signal having been applied to the first signal line 11 i,electric charges thus charged in the liquid crystal capacitance and theauxiliary capacitance are kept as they are even after the thin filmtransistor 14 is turned off. Hence, images can be displayed in a screen.

As illustrated in FIG. 2, the thin film transistor 14 is generallyformed in the vicinity of an intersection of the first signal line 11 iwith the scanning line 12. In such arrangement, the pixel electrode 13is formed with a cut-out portion in order to avoid interference of thepixel electrode 13 with the thin film transistor 14. The cut-out portionhas a length Lt in a direction in which the first signal line 11 iextends.

As a result, a length Li along which the pixel electrode 13 is adjacentto the first signal line 11 i is not equal to a length Lj along whichthe pixel electrode 13 is adjacent to the second signal line 11 j.Accordingly, if a space di between the pixel electrode 13 and the firstsignal line 11 i is equal to a space dj between the pixel electrode 13and the second signal line 11 j, the parasitic capacitance Cd-pijgenerated between the pixel electrode 13 and the second signal line 11 jis greater than the parasitic capacitance Cd-pii generated between thepixel electrode 13 and the first signal line 11 i (Cd-pii<Cd-pij), whichis not preferable because voltage of the pixel electrode 13 isinfluenced by fluctuation in voltage in the signal lines.

In order to solve this problem, Japanese Unexamined Patent PublicationNo. 5-80353 has suggested various solutions as follows.

First, Japanese Unexamined Patent Publication No. 5-80353 has suggesteda method of equalizing parasitic capacitances to each other by setting aspace dj between the pixel electrode 13 and the second signal line 11 jto be greater than a space between the pixel electrode 13 and the firstsignal line 11 i (di<dj), to thereby ensure that a parasitic capacitanceper a unit length between the pixel electrode 13 and the first signalline 11 i is greater than the same between the pixel electrode 13 andthe second signal line 11 j.

However, since the pixel electrode 13 is separately exposed to lightfrom the first and second signal lines 11 i and 11 j in this method, thespaces di and dj are not always formed equal to designed values due tomisalignment of masks in exposure. As a result, the parasiticcapacitances are not coincident with each other.

In order to equalize the parasitic capacitances to each other, it wouldbe necessary to design the spaces di and dj so wide that influencecaused by misalignment of masks can be ignored. However, thissignificantly reduces a numerical aperture (NA).

Secondly, Japanese Unexamined Patent Publication No. 5-80353 hassuggested a method of equalizing the parasitic capacitances to eachother, in which a space dj between the pixel electrode 13 and the secondsignal line 11 j is divided into two regions in one of which the spacedj is designed to be equal to a space di between the pixel electrode 13and the first signal line 11 i, and in the other of which the space djis greater than the space di.

However, this second method cannot sufficiently equalize the parasiticcapacitances to each other for the same reason as the above-mentionedfirst method.

Thirdly, Japanese Unexamined Patent Publication No. 5-80353 hassuggested a liquid crystal display device in which the first signal line11 i is designed to have a projection to ensure that a length alongwhich the pixel electrode 13 is adjacent to the first signal line 11 iis equal to a length along which the pixel electrode 13 is adjacent tothe second signal line 11 j.

However, the suggested liquid crystal display device is accompanied witha problem that the parasitic capacitances are not equal to each otherdue to misalignment of masks.

Fourthly, Japanese Unexamined Patent Publication No. 5-80353 hassuggested a liquid crystal display device designed to include aparasitic capacity compensator. In the suggested liquid crystal displaydevice, a signal line branches away. The parasitic capacity compensatoris comprised of a branching portion and the signal line which partiallyinterpose a pixel electrode therebetween.

In accordance with the liquid crystal display device, theabove-mentioned problem of misalignment of masks can be solved. However,it is necessary in the liquid crystal display device to design a spacebetween the pixel electrode and the branching portion of the signal linein the parasitic capacity compensator smaller than a space between thepixel electrode and the signal line.

In addition, when the signal lines and the pixel electrode are formed ina common layer, they have to be spaced away from each other to somedegree in order to avoid short-circuit therebetween. Thus, there is acritical space between the signal lines and the pixel electrode. Hence,if such a critical space is applied to the above-mentioned parasiticcapacity compensator, it would be necessary to space the pixel electrodefrom the signal lines by a distance greater than the critical space.However, this results in reduction in an area of the pixel electrode,which unpreferably causes reduction in a numerical aperture.

Fifthly, Japanese Unexamined Patent Publication No. 5-80353 hassuggested a liquid crystal display device in which the parasiticcapacity compensator is overlapped the pixel electrode with aninsulating film being sandwiched therebetween, and the parasiticcapacitances are compensated for by electrostatic capacitance of anoverlapping portion of the parasitic capacity compensator.

In accordance with the liquid crystal display device, the problem havingbeen mentioned in the fourth suggestion can be solved. However, thefifth suggestion cannot be applied to a liquid crystal display device inwhich the pixel electrode and the signal lines are formed in a commonlayer.

Japanese Unexamined Patent Publication No. 6-274130 has suggested aliquid crystal display device comprised of (a) a first substrateincluding a switching device, a light-permeable pixel electrodeelectrically connected to a terminal of the switching device, a firstsignal line, a second signal line extending adjacently to the firstsignal line, and a third signal line through which a signal for turningthe switching device on or off is transmitted, (b) a second substrate onwhich an opposing electrode is formed, (c) a drive circuit which appliesa signal to the second signal line which signal has a polarity oppositeto a polarity of a signal to be applied to the first signal line, and(d) a liquid crystal layer sandwiched between the first and secondsubstrates, the pixel electrode overlapping the first and second signallines with an insulating thin film being sandwiched therebetween.

However, the suggested liquid crystal display device is accompanied withthe above-mentioned problem that a parasitic capacitance generatedbetween the pixel electrode and the first signal line is not equal to aparasitic capacitance between the pixel electrode and the second signalline due to a difference in length between a length along which thepixel electrode is adjacent to the first signal line and a length alongwhich the pixel electrode is adjacent to the second signal line.

SUMMARY OF THE INVENTION

In view of the above-mentioned problems in the conventional liquidcrystal display devices, it is an object of the present invention toprovide a liquid crystal display device which is capable of minimizingimbalance in parasitic capacitances to be generated between a pixelelectrode and first and second signal lines, and hence, ensuring nofluctuation in brightness.

It is also an object of the present invention to provide a method offabricating such a liquid crystal display device.

In one aspect of the present invention, there is provided a liquidcrystal display device including (a) a pixel electrode, (b) a firstsignal line extending along one side of the pixel electrode, and (c) asecond signal line extending along the other side of the pixelelectrode, a first length along which the pixel electrode and the firstsignal line are adjacent to each other being equal to a second lengthalong which the pixel electrode and the second signal line are adjacentto each other, a first space between the pixel electrode and the firstsignal line being equal to a second space between the pixel electrodeand the second signal line.

It is preferable that the pixel electrode includes a region having beenexposed to light, at a periphery thereof.

It is preferable that the pixel electrode is formed in a layer in whichthe first and second signal lines are also formed.

It is preferable that the first and second signal lines are formed in afirst layer, and the pixel electrode is formed in a second layer whichis electrically isolated from the first layer by an insulating layersandwiched between the first and second layers.

There is further provided a liquid crystal display device including (a)a pixel electrode, (b) a first signal line extending along one side ofthe pixel electrode, and (c) a second signal line extending along theother side of the pixel electrode, at least one of the first and secondsignal lines having a projecting portion extending towards the pixelelectrode, a first length along which the pixel electrode and the firstsignal line are adjacent to each other being equal to a second lengthalong which the pixel electrode and the second signal line are adjacentto each other, a first space between the pixel electrode and the firstsignal line being equal to a second space between the pixel electrodeand the second signal line.

There is still further provided a liquid crystal display deviceincluding (a) a pixel electrode, (b) a thin film transistor locatedadjacent to the pixel electrode and at one side of the pixel electrode,(c) a first signal line extending along the one side of the pixelelectrode, and (d) a second signal line extending along the other sideof the pixel electrode, the pixel electrode being formed with a cut-outportion at the other side thereof, the cut-out portion having a lengthequal to a length along which the first signal line cannot be adjacentto the pixel electrode by the thin film transistor, a first length alongwhich the pixel electrode and the first signal line are adjacent to eachother being equal to a second length along which the pixel electrode andthe second signal line are adjacent to each other, a first space betweenthe pixel electrode and the first signal line being equal to a secondspace between the pixel electrode and the second signal line.

There is yet further provided a liquid crystal display device including(a) a plurality of pixel electrodes each spaced away from adjacent onesby a predetermined distance, (b) first signal lines each extending alongone side of each of the pixel electrodes, each of the first signal lineshaving a bending portion which extends along a periphery of each of thepixel electrodes, and (c) second signal lines each extending along theother side of each of the pixel electrodes, each of the second signallines having a bending portion which extends along a periphery of eachof the pixel electrodes, at least one of the first and second signallines having a projecting portion extending towards the pixel electrode,a first length along which the pixel electrode and the first signal lineare adjacent to each other being equal to a second length along whichthe pixel electrode and the second signal line are adjacent to eachother, a first space between the pixel electrode and the first signalline being equal to a second space between the pixel electrode and thesecond signal line.

In another aspect of the present invention, there is provided a methodof fabricating a liquid crystal display device including a pixelelectrode, a first signal line extending along one side of the pixelelectrode, and a second signal line extending along the other side ofthe pixel line, including the steps of (a) forming a scanning line on atransparent substrate, and then, forming a gate insulating film on thescanning line and the transparent substrate, (b) forming a channel onthe gate insulating film above the scanning line, (c) forming the firstand second signal lines so that a first length along which the pixelelectrode and the first signal line are adjacent to each other is equalto a second length along which the pixel electrode and the second signalline are adjacent to each other, and a first space between the pixelelectrode and the first signal line is equal to a second tin spacebetween the pixel electrode and the second signal line, (d) forming thepixel electrode, and (e) covering a product resulting from the step (d)with an insulating film.

It is preferable that the pixel electrode is formed between the firstand second signal lines in a common layer in the step (d).

It is preferable that the pixel electrode is formed, after theinsulating film has been formed, on the insulating film above a regionsandwiched between the first and second signal lines.

There is further provided a method of fabricating a liquid crystaldisplay device including a pixel electrode, a first signal lineextending along one side of the pixel electrode, and a second signalline extending along the other side of the pixel line, including thesteps of (a) forming a scanning line on a transparent substrate, andthen, forming a gate insulating film on the scanning line and thetransparent substrate, (b) forming a channel on the gate insulating filmabove the scanning line, (c) forming the first and second signal linesso that at least one of the first and second signal lines has aprojecting portion extending towards the pixel electrode and that afirst length along which the pixel electrode and the first signal lineare adjacent to each other is equal to a second length along which thepixel electrode and the second signal line are adjacent to each other,and a first space between the pixel electrode and the first signal lineis equal to a second space between the pixel electrode and the secondsignal line, (d) forming the pixel electrode, and (e) covering a productresulting from the step (d) with an insulating film.

There is still further provided a method of fabricating a liquid crystaldisplay device including a pixel electrode, a first signal lineextending along one side of the pixel electrode, and a second signalline extending along the other side of the pixel line, including thesteps of (a) forming a scanning line on a transparent substrate, andthen, forming a gate insulating film on the scanning line and thetransparent substrate, (b) forming a channel on the gate insulating filmabove the scanning line, (c) forming the first and second signal linesso that at least one of the first and second signal lines has a cut-outportion having a length equal to a length along which the first and/orsecond signal line(s) cannot be adjacent to the pixel electrode by athin film transistor formed at one side of the pixel electrode, thecut-put portion being formed at the other side of the pixel electrode, afirst length along which the pixel electrode and the first signal lineare adjacent to each other being equal to a second length along whichthe pixel electrode and the second signal line are adjacent to eachother, a first space between the pixel electrode and the first signalline being equal to a second space between the pixel electrode and thesecond signal line, (d) forming the pixel electrode, and (e) covering aproduct resulting from the step (d) with an insulating film.

There is yet further provided a method of fabricating a liquid crystaldisplay device including a plurality of pixel electrodes each spacedaway from adjacent ones by a predetermined distance, first signal lineseach extending along one side of each of the pixel electrodes, each ofthe first signal lines having a bending portion which extends along aperiphery of each of the pixel electrodes, and second signal lines eachextending along the other side of each of the pixel electrodes, each ofthe second signal lines having a bending portion which extends along aperiphery of each of the pixel electrodes, including the steps of (a)forming a scanning line on a transparent substrate, and then, forming agate insulating film on the scanning line and the transparent substrate,(b) forming a channel on the gate insulating film above the scanningline, (c) forming the first and second signal lines so that at least oneof each of the first signal lines and each of second signal lines has aprojecting portion extending towards each of the pixel electrodes andthat a first length along which each of the pixel electrodes and each ofthe first signal lines are adjacent to each other is equal to a secondlength along which each of the pixel electrodes and each of the secondsignal lines are adjacent to each other, and a first space between eachof the pixel electrodes and each of the first signal lines is equal to asecond space between each of the pixel electrodes and each of the secondsignal lines, (d) forming the pixel electrodes, and (e) covering aproduct resulting from the step (d) with an insulating film.

The advantages obtained by the aforementioned present invention will bedescribed hereinbelow.

In accordance with the present invention, it is possible to equalizeparasitic capacitances generated between a pixel electrode and signallines to each other.

As mentioned earlier, spaces between a pixel electrode and signal linesmay be different from each other due to misalignment of masks whichmight occur when a pixel electrode is exposed to light separately fromsignal lines. In accordance with the present invention, the parasiticcapacitances can be equalized to each other without being influenced bymisalignment of masks.

Accordingly, the present invention makes it possible to preventfluctuation in brightness of a pixel which fluctuation is caused byimbalance in parasitic capacitances between a pixel electrode and signallines.

The above and other objects and advantageous features of the presentinvention will be made apparent from the following description made withreference to the accompanying drawings, in which like referencecharacters designate the same or similar parts throughout the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a circuit equivalent to a pixel in anactive matrix type liquid crystal display device.

FIG. 2 is a plan view of a pixel in a conventional liquid crystaldisplay device.

FIG. 3A illustrates polarity of pixel electrodes in a screen in acertain display-updating period in gate line inversion drive.

FIG. 3B illustrates polarity of pixel electrodes in a screen in a nextdisplay-updating period both in gate line inversion drive.

FIG. 4A illustrates polarity of pixel electrodes in a screen in acertain display-updating period in drain line inversion drive.

FIG. 4B illustrates polarity of pixel electrodes in a screen in a nextdisplay-updating period both in drain line inversion drive.

FIG. 5A illustrates polarity of pixel electrodes in a screen in acertain display-updating period.

FIG. 5B illustrates polarity of pixel electrodes in a screen in a nextdisplay-updating period both in dot inversion drive.

FIG. 6 is a plan view of a TFT substrate in a liquid crystal displaydevice in accordance with the first embodiment of the present invention.

FIG. 7 is a cross-sectional view taken along the line VII—VII in FIG. 6.

FIG. 8 is a cross-sectional view taken along the line VIII—VIII in FIG.6.

FIG. 9 is a plan view of a TFT substrate in a liquid crystal displaydevice in accordance with the second embodiment of the presentinvention.

FIG. 10 is a cross-sectional view taken along the line X—X in FIG. 9.

FIG. 11 is a plan view of a TN substrate in a liquid crystal displaydevice in accordance with the third embodiment of the present invention.

FIG. 12 is a plan view of a TFT substrate in a liquid crystal displaydevice in accordance with the fourth embodiment of the presentinvention.

FIG. 13 is a flow chart of a method of fabricating the liquid crystaldisplay device in accordance with the first, third or fourth embodiment.

FIG. 14 is a partial flow chart of a method of fabricating the liquidcrystal display device in accordance with the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 6, 7 and 8 illustrate a liquid crystal display device inaccordance with the first embodiment. FIG. 6 is a plan view of a TFTsubstrate in the liquid crystal display device, FIG. 7 is across-sectional view taken along the line VII—VII in FIG. 6, and FIG. 8is a cross-sectional view taken along the line VIII—VIII in FIG. 6.

As illustrated in FIG. 6, the liquid crystal display device is comprisedof a pixel electrode 13, a first signal line 11 i extending along oneside of the pixel electrode 13, a second signal line 11 j extendingalong the other side of the pixel electrode 13, and a thin filmtransistor (TFT) 14 located at a corner of the pixel electrode 13 andbetween the pixel electrode 13 and the first signal line 11 i.

The pixel electrode 13 includes a pixel edge section 13 a which definesan outer edge of the pixel electrode 13, and is located adjacent to thefirst and second signal lines 11 i and 11 j through the pixel edgesection 13 a. The pixel edge section 13 a is formed by being exposed tolight simultaneously with the first and second signal lines 11 i and 11j.

A scanning line 12 extends perpendicularly to the first and secondsignal lines 11 i and 11 j. A gate electrode (not illustrated) of thethin film transistor 14 is electrically connected to the scanning line12.

The first signal line 11 i is formed with a projecting portion 11 aprojecting towards the pixel electrode 13. The projecting portion 11 ais designed to have such a length that a first length along which thepixel electrode 13 is adjacent to the first signal line 11 i is equal toa second length along which the pixel electrode 13 is adjacent to thesecond signal line 11 j. That is, assuming that a length along which thepixel electrode 13 is vertically adjacent to the first signal line 11 iis represented with “La”, a length along which the pixel electrode 13 ishorizontally adjacent to the projecting portion 11 a is represented with“Lb”, a length along which the pixel electrode 13 is vertically adjacentto the projecting portion 11 a is represented with “Lc”, and a lengthalong which the pixel electrode 13 is adjacent to the second signal line11 j is represented with “L”, the projecting portion 11 a is designed tomeet the following equation.

La+Lb+Lc=L  (A)

A space “d” between the pixel edge section 13 a and the first signalline 11 i including the projecting 11 a is equal anywhere to a space “d”between the pixel edge section 13 a and the second signal line 11 j.

In accordance with the first embodiment, a parasitic capacitancegenerated between the pixel electrode 13 and the first signal line 11 iis equal to a parasitic capacitance generated between the pixelelectrode 13 and the second signal line 11 j. This is not influenced byvariance produced in fabrication steps.

Hence, the first embodiment makes it possible to prevent fluctuation inbrightness of a pixel which fluctuation is caused by imbalance in aparasitic capacitance between the pixel electrode and the signal lines,ensuring high quality in display.

Though the first signal line 11 i is designed to have the projectingportion 11 a in the first embodiment, it should be noted that the secondsignal line 11 j may be designed to have the projecting portion 11 a. Asan alternative, the projecting portion 11 a may be formed both in thefirst and second signal lines 11 i and 11 j.

Hereinbelow is explained a method of fabricating the liquid crystaldisplay device illustrated in FIG. 6 with reference to FIGS. 7, 8 and13.

First, as illustrated in FIG. 7, a pattern of a scanning line 12composed of electrically conductive material such as metal is formed ona glass substrate 31 in step 100.

Then, a gate insulating film 32 composed of electrically insulatingmaterial such as silicon nitride is formed all over the glass substrate31 and the scanning line pattern 12 in step 110.

Then, an amorphous silicon layer 33 which will make a channel of atransistor is formed on the gate insulating film 32 above the scanningline pattern 12 in step 120. Then, a contact layer 35 is formed on theamorphous silicon layer 33 in step 130 in order to establish electricalconnection between the channel and later formed drain electrode 14 a andsource electrode 14 b.

Then, the first signal line 11 i is formed on the gate insulating film32 as illustrated in FIG. 7, and the second signal line 11 j is formedon the gate insulating film 32 as illustrated in FIG. 8. Both the firstand second signal lines 11 i and 11 j are composed of electricallyconductive material such as metal. The first and/or second signalline(s) 11 i and 11 j are(is) formed to have a projecting portion 11 ain step 140 so that the above-mentioned equation (A) is established,that is, a first length along which the pixel electrode 13 is adjacentto the first signal line 11 i is equal to a second length along whichthe pixel electrode 13 is adjacent to the second signal line 11 j.

Simultaneously with the first and second signal lines 11 i and 11 j areformed the pixel edge section 13 a through which the pixel electrode 13is adjacent to the first and second signal lines 11 i and 11 j, a drainelectrode 14 a, and a source electrode 14 b in step 140.

The pixel edge section 13 a is formed in such a manner that a space “d”between the pixel edge section 13 a and the first and second signallines 11 i and 11 j is constant anywhere.

At this stage, the pixel edge section 13 a may be electrically connectedto the source electrode 14 b, or may not.

Then, there is formed the pixel electrode 13 within the pixel edgesection 13 a so that the pixel electrode 13 makes contact with the pixeledge section 13 a, in step 150. The pixel electrode 13 is composed ofelectrically conductive transparent material such as indium-tin-oxide(ITO). The pixel electrode 13 is formed so as to electrically connectwith the pixel edge section 13 a and the source electrode 14 b, and soas to be located remoter from the first and second signal lines 11 i and11 j than the pixel edge section 13 a.

Since the contact layer 35 bridges over the drain electrode 14 a and thesource electrode 14 b, the drain electrode 14 a is kept in electricalconnection with the source electrode 14 b, if the contact layer 35 iskept as it is. Hence, a portion 35 a of the contact layer 35 is removedbetween the drain electrode 14 a and the source electrode 14 b in step160.

Then, as illustrated in FIGS. 7 and 8, an insulating protection film 36composed of insulating material such as silicon nitride is deposited allover the liquid crystal display device in step 170. The insulatingprotection film 36 is not illustrated in FIG. 6 for simplification.

Then, unnecessary portions of the insulating protection film 36 areremoved in step 180. Thus, a TFT substrate of the liquid crystal displaydevice in accordance with the first embodiment is completed.

In accordance with the first embodiment, it is possible to equalize theparasitic capacitance generated between the pixel electrode 13 and thefirst signal line 11 i to the parasitic capacitance generated betweenthe pixel electrode 13 and the second signal line 11 j.

In the conventional liquid crystal display device illustrated in FIG. 2,the space di between the pixel electrode 13 and the first signal line 11i may be different from the space dj between the pixel electrode 13 andthe second signal line 11 j due to misalignment of masks which mightoccur when the pixel electrode 13 is exposed to light separately fromthe first and second signal lines 11 i and 11 j. However, in accordancewith the first embodiment, the parasitic capacitances can be equalizedto each other without being influenced by misalignment of masks.

Accordingly, the first embodiment makes it possible to preventfluctuation in brightness of a pixel which fluctuation is caused byimbalance in parasitic capacitances between the pixel electrode 13 andthe signal lines 11 i and 11 j, ensuring high quality in display.

Though the present invention is applied in the first embodiment to achannel etch type amorphous silicon TFT having a bottom gate structure,it should be noted that the present invention is not to be limited tothe structure having been mentioned in the first embodiment. Forinstance, the present invention may be applied to a channel protectiontype amorphous silicon TFT or a polysilicon TFT.

As an alternative, the present invention may be applied to a liquidcrystal display device including a non-linear element such as MIM as adriver element.

FIG. 9 is a plan view of a TFT substrate in the liquid crystal displaydevice in accordance with the second embodiment. FIG. 10 is across-sectional view taken along the line X—X in FIG. 9.

As illustrated in FIG. 9, the liquid crystal display device is comprisedof a pixel electrode 13, a first signal line 11 i extending along oneside of the pixel electrode 13, a second signal line 11 j extendingalong the other side of the pixel electrode 13, and a thin filmtransistor (TFT) 14 located at a corner of the pixel electrode 13 andbetween the pixel electrode 13 and the first signal line 11 i.

The liquid crystal display device in accordance with the secondembodiment has basically the same structure as that of the liquidcrystal display device in accordance with the first embodiment. However,the second embodiment is different from the first embodiment withrespect to fabrication steps. In the liquid crystal display device inaccordance with the second embodiment, the pixel electrode 13 is formedafter the formation of the insulating protection film 36 and the removalof unnecessary portions thereof. That is, the pixel electrode 13 and thefirst and second signal lines 11 i and 11 j are formed in a common layerin the first embodiment, as illustrated in FIGS. 7 and 8, whereas thepixel electrode 13 is formed in a layer separate from a layer in whichthe first and second signal lines 11 i and 11 j are formed, in thesecond embodiment, as illustrated in FIG. 10.

In FIG. 10, a thickness of the insulating protection film 36 isillustrated in exaggeration. In general, the insulating protection film36 has a thickness of about 50 nm. A minimum space by which the pixeledge section 13 a are spaced away from the first and second signal lines11 i and 11 j without short-circuiting each other is generally in therange of 3 μm to 4 μm (3,000 nm to 4,000 nm). Hence, even if the pixelelectrode 13 is formed in a layer separate from a layer in which thefirst and second signal lines 11 i and 11 j are formed, with theinsulating protection film 36 being sandwiched between those layers, thesecond embodiment can provide the same advantages as those obtained bythe first embodiment.

Though not illustrated, the pixel electrode 13 is designed to makeelectrical contact with the pixel edge section 13 at a certain point.

FIG. 14 is a flow chart of a method of fabricating the liquid crystaldisplay device in accordance with the second embodiment.

The method has the same steps 100 to 140 illustrated in FIG. 13. In thismethod, after the step 140 has been carried out, a portion 35 a of thecontact layer 35 between the drain electrode 14 a and the sourceelectrode 14 b is removed in step 190.

Then, the insulating protection film 36 composed of electricallyinsulating material such as silicon nitride is deposited all over theliquid crystal display device in step 200. Thereafter, unnecessaryportions of the insulating protection film 36 are removed in step 210.

Then, as illustrated in FIG. 10, there is formed the pixel electrode 13within the pixel edge section 13 a so that the pixel electrode 13 makescontact with the pixel edge section 13 a, in step 220. The pixelelectrode 13 is composed of electrically conductive transparent materialsuch as indium-tin-oxide (ITO). The pixel electrode 13 is formed so asto electrically connect with the pixel edge section 13 a and the sourceelectrode 14 b, and so as to be located remoter from the first andsecond signal lines 11 i and 11 j than the pixel edge section 13 a.

Thus, there is completed a TFT substrate of the liquid crystal displaydevice in accordance with the second embodiment.

FIG. 11 is a plan view of a TFT substrate in the liquid crystal displaydevice in accordance with the third embodiment.

The liquid crystal display device in accordance with the thirdembodiment is structurally different from the liquid crystal displaydevice in accordance with the first embodiment in that the pixelelectrode 13 and the pixel edge section 13 a are formed with a cut-outportion 15 in place of the projecting portion 11 a formed at the firstsignal line 11 i.

As illustrated in FIG. 11, the cut-out portion 15 is formed at a cornerof the pixel electrode 13 at a side opposite to a side at which the thinfilm transistor 14 is formed.

The cut-out portion 15 is designed to have a length in a direction inwhich the signal lines 11 i and 11 j extend which length is equal to alength by which the first signal line 11 i cannot be adjacent to thepixel electrode 13 due to presence of the thin film transistor 14.Accordingly, a first length L1 along which the pixel electrode 13 isadjacent to the first signal line 11 i is equal to a second length L2along which the pixel electrode 13 is adjacent to the second signal line11 j (L1=L2).

The pixel electrode 13 and the signal lines 11 i and 11 j may be formedin a common layer similarly to the first embodiment, or may be formed inseparate layers similarly to the second embodiment.

In a method of fabricating the liquid crystal display device inaccordance with the third embodiment, the step 140 a is carried out inplace of the step 140 in the method of fabricating the liquid crystaldisplay device in accordance with the first embodiment, illustrated inFIG. 13. The steps 100 to 130 and 150 to 180 are carried out similarlyto the first embodiment.

In the step 140 a, the first and second signal lines 11 i and 11 j areformed, and there is also formed the pixel edge section 13 a having thecut-out portion 15 at a corner thereof at a side opposite to a side atwhich the thin film transistor 14 is formed. The cut-out portion 15 isdesigned to have such a length that a first length L1 along which thepixel electrode 13 is adjacent to the first signal line 11 i is equal toa second length L2 along which the pixel electrode 13 is adjacent to thesecond signal line 11 j (L1=L2).

In addition, the drain electrode 14 a and the source electrode 14 b areformed at the same time.

In the step 150, the pixel electrode 13 is formed so as to have thecut-out portion 15 in harmony with the cut-out portion 15 formed at thepixel edge section 13 a.

The pixel electrode 13 and the signal lines 11 i and 11 j in the thirdembodiment may be formed in separate layers, in which case, the stepsillustrated in FIG. 14 are carried out in the same order as that of thesecond embodiment.

FIG. 12 is a plan view of a TFT substrate in the liquid crystal displaydevice in accordance with the fourth embodiment.

In the fourth embodiment, the pixel electrodes 13 are arranged indelta-arrangement in which a line of the pixel electrodes 13 sandwichedbetween adjacent scanning lines 12 are deviated by half-pitch from anadjacent line of the pixel electrodes 13.

In a liquid crystal display device arranged in delta-arrangement, asillustrated in FIG. 12, it is necessary to design the first and secondsignal lines 11 i and 11 j not to interfere with the pixel electrode 13.Accordingly, the first and second signal lines 11 i and 11 j have abending portion in harmony with a shape of the pixel electrode 13.Hence, a length L1 along which the pixel electrode 13 is adjacent to thefirst signal line 11 i is generally remarkably different from a lengthL2 along which the pixel electrode 13 is adjacent to the second signalline 11 j, resulting in that a voltage of the pixel electrode 13 issignificantly influenced by voltages of the first and second signallines 11 i and 11 j.

In order to solve such a problem, the second signal line 11 j in thefourth embodiment is formed with a projecting portion 11 a projectingtowards the pixel electrode 13, to thereby ensure that a first length L1along which the pixel electrode 13 is adjacent to the first signal line11 i is equal to a second length L2 along which the pixel electrode 13is adjacent to the second signal line 11 j (L1=L2).

In addition, the pixel edge section 13 a is exposed to lightconcurrently with the first and second signal lines 11 i and 11 j, whichensures that a voltage of the pixel electrode 13 is less influenced byvoltages of the first and second signal lines 11 i and 11 j.

The pixel electrode 13 and the signal lines 11 i and 11 j may be formedin a common layer similarly to the above-mentioned embodiments, in whichease, the steps illustrated in FIG. 13 are carried out in the same orderas having been explained earlier with reference to FIG. 13. As analternative, the pixel electrode 13 and the signal lines 11 i and 11 jmay be formed in separate layers, in which case, the steps illustratedin FIG. 14 are carried out in the same order as having been explainedearlier with reference to FIG. 14.

While the present invention has been described in connection withcertain preferred embodiments, it is to be understood that the subjectmatter encompassed by way of the present invention is not to be limitedto those specific embodiments. On the contrary, it is intended for thesubject matter of the invention to include all alternatives,modifications and equivalents as can be included within the spirit andscope of the following claims.

The entire disclosure of Japanese Patent Application No. 10-271140 filedon Sep. 25, 1998 including specification, claims, drawings and summaryis incorporated herein by reference in its entirety.

What is claimed is:
 1. A liquid crystal display device comprising: (a) apixel electrode, wherein said pixel electrode includes a pixel edgesection; (b) a thin film transistor located adjacent to said pixelelectrode and at one side of said pixel electrode; (c) a first signalline extending along said one side of said pixel electrode; and (d) asecond signal line extending along the other side of said pixelelectrode, said pixel electrode being formed with a cut-out portion atthe other side thereof, said cut-out portion having a length equal to alength along which said first signal line cannot be adjacent to saidpixel electrode by said thin film transistor, a first length along whichsaid pixel electrode and said first signal line are adjacent to eachother being equal to a second length along which said pixel electrodeand said second signal line are adjacent to each other, a first spacebetween said pixel edge section and said first signal line being equalto a second space between said pixel edge section and said second signalline.
 2. The liquid crystal display device as set forth in claim 1,wherein said pixel electrode is formed on a layer in which said firstand second signal lines are also formed.
 3. The liquid crystal displaydevice as set forth in claim 1, wherein said first and second signallines are formed on a first layer, and said pixel electrode is formed ona second layer which is electrically isolated from said first layer byan insulating layer sandwiched between said first and second layers. 4.A liquid crystal display device comprising: (a) a plurality of pixelelectrodes each spaced away from adjacent ones by a predetermineddistance, wherein said pixel electrodes include pixel edge sections; (b)first signal lines each extending along one side of each of said pixelelectrodes, each of said first signal lines having a bending portionwhich extends along a periphery of each of said pixel electrodes; and(c) second signal lines each extending along the other side of each ofsaid pixel electrodes, each of said second signal lines having a bendingportion which extends along a periphery of each of said pixelelectrodes, at least one of said first and second signal lines having aprojecting portion extending towards said pixel electrodes, a firstlength along which said pixel electrodes and said first signal lines areadjacent to each other being equal to a second length along which saidpixel electrodes and said second signal lines are adjacent to eachother, a first space between said pixel edge sections and said firstsignal lines being equal to a second space between said pixel edgesections and said second signal lines.
 5. The liquid crystal displaydevice as set forth in claim 4, wherein each of said pixel electrodes isformed on a layer in which said first and second signal lines are alsoformed.
 6. The liquid crystal display device as set forth in claim 4,wherein said first and second signal lines are formed on a first layer,and said pixel electrodes are formed on a second layer which iselectrically isolated from said first layer by an insulating layersandwiched between said first and second layers.
 7. A method offabricating a liquid crystal display device including a pixel electrode,a pixel edge section, a first signal line extending along one side ofsaid pixel electrode, and a second signal line extending along the otherside of said pixel electrode, comprising the steps of: (a) forming ascanning line on a transparent substrate, and then, forming a gateinsulating film on said scanning line and said transparent substrate;(b) forming a channel on said gate insulating film above said scanningline; (c) forming said pixel edge section and said first and secondsignal lines so that a first length along which said pixel electrode andsaid first signal line are adjacent to each other is equal to a secondlength along which said pixel electrode and said second signal line areadjacent to each other, and a first space between said pixel edgesection and said first signal line is equal to a second space betweensaid pixel edge section and said second signal line, (d) forming saidpixel electrode; and (e) covering a product resulting from said step (d)with an insulating layer.
 8. The method as set forth in claim 7, whereinsaid pixel electrode is formed between said first and second signallines on a common layer in said step (d).
 9. The method as set forth inclaim 8, wherein said pixel electrode is formed, after said gateinsulating film has been formed, on said gate insulating film above aregion sandwiched between said first and second signal lines.
 10. Amethod of fabricating a liquid crystal display device including a pixelelectrode, a pixel edge section, a first signal line extending along oneside of said pixel electrode, and a second signal line extending alongthe other side of said pixel electrode, comprising the steps of: (a)forming a scanning line on a transparent substrate, and then, forming agate insulating film on said scanning line and said transparentsubstrate; (b) forming a channel on said gate insulating film above saidscanning line; (c) forming said pixel edge section and said first andsecond signal lines so that at least one of said first and second signallines has a projecting portion extending towards said pixel electrodeand that a first length along which said pixel electrode and said firstsignal line are adjacent to each other is equal to a second length alongwhich said pixel electrode and said second signal line are adjacent toeach other, and a first space between said pixel edge section and saidfirst signal line is equal to a second space between said pixel edgesection and said second signal line, (d) forming said pixel electrode;and (e) covering a product resulting from said step (d) with aninsulating layer.
 11. The method as set forth in claim 10, wherein saidpixel electrode is formed between said first and second signal lines ona common layer in said step (d).
 12. The method as set forth in claim10, wherein said pixel electrode is formed, after said gate insulatingfilm has been formed, on said gate insulating film above a regionsandwiched between said first and second signal lines.
 13. A method offabricating a liquid crystal display device including a pixel electrode,a pixel edge section, a first signal line extending along one side ofsaid pixel electrode, and a second signal line extending along the otherside of said pixel electrode, comprising the steps of: (a) forming ascanning line on a transparent substrate, and then, forming a gateinsulating film on said scanning line and said transparent substrate;(b) forming a channel on said gate insulating film above said scanningline; (c) forming said pixel edge section with a cut-out portion andforming said first and second signal lines so that said cut-out portionhas a length equal to a length along which said first and/or secondsignal line(s) cannot be adjacent to said pixel electrode by a thin filmtransistor formed at one side of said pixel electrode, a first lengthalong which said pixel electrode and said first signal line are adjacentto each other being equal to a second length along which said pixelelectrode and said second signal line are adjacent to each other, afirst space between said pixel electrode and said first signal linebeing equal to a second space between said pixel electrode and saidsecond signal line, (d) forming said pixel electrode; and (e) covering aproduct resulting from said step (d) with an insulating layer.
 14. Themethod as set forth in claim 13, wherein said pixel electrode is formedbetween said first and second signal lines on a common layer in saidstep (d).
 15. The method as set forth in claim 13, wherein said pixelelectrode is formed, after said gate insulating film has been formed, onsaid sate insulating film above a region sandwiched between said firstand second signal lines.
 16. A method of fabricating a liquid crystaldisplay device including a plurality of pixel electrodes each spacedaway from adjacent ones by a predetermined distance, said pixelelectrodes having pixel edge sections, first signal lines each extendingalong one side of each of said pixel electrodes, each of said firstsignal lines having a projecting portion which extends along a peripheryof each of said pixel electrodes, and second signal lines each extendingalong the other side of each of said pixel electrodes, each of saidsecond signal lines having a projecting portion which extends along aperiphery of each of said pixel electrodes, comprising the steps of: (a)forming a scanning line on a transparent substrate, and then, forming agate insulating film on said scanning line and said transparentsubstrate; (b) forming a channel on said gate insulating film above saidscanning line; (c) forming said pixel edge sections and said first andsecond signal lines so that at least one of each of said first signallines and each of said second signal lines has a projecting portionextending towards each of said pixel electrodes and that a first lengthalong which each of said pixel electrodes and each of said first signallines are adjacent to each other is equal to a second length along whicheach of said pixel electrodes and each of said second signal lines areadjacent to each other, and a first space between each of said pixeledge sections and each of said first signal lines is equal to a secondspace between each of said pixel edge sections and each of said secondsignal lines, (d) forming said pixel electrodes; and (e) covering aproduct resulting from said step (d) with an insulating layer.
 17. Themethod as set forth in claim 16, wherein each of said pixel electrodesis formed between each of said first signal lines and each of saidsecond signal lines on a common layer in said step (d).
 18. The methodas set forth in claim 16, wherein each of said pixel electrodes isformed, after said gate insulating film has been formed, on said gateinsulating film above a region sandwiched between said first and secondsignal lines.